Process of stretching polyacrylonitrile filaments



U.S. Cl. 26428 Claim ABSTRACT OF THE DISCLOSURE The process for treatingfibres produced from acrylonitrile polymers which contain from 85 to 97percent by weight of acrylonitrile which comprises stretching the fibresto at least 5 times their initial length and quenching them immediatelythereafter by bringing them to a temperature between about 30 C. andabout 0 C. preferably in water. It is particularly preferred that thefibres are brought to a temperature of less than C.

This invention relates to the treatment of fibres produced fromacrylonitrile polymers, and in particular to the treatment of fibresproduced from acrylonitrile polymers containing from 85 percent to 97percent by weight of acrylonitrile units.

Fibres produced from acrylonitrile polymers are stretched afterspinning, and are commonly washed after stretching and subsequentlydried. Irregularities in physical properties of the resulting fibres aresometimes noted, and there is some tendency to fibrillation,particularly with fibres of heavy denier, such as those larger thandenier for example, and with the fibres which have been spun frompolymer compositions containing certain additives including someflame-retarding additives.

According to this invention, a process for the treatment of fibresproduced from acrylonitrile polymers containing from 85 percent to 97percent by weight of acrylonitrile units comprises stretching the fibresin steam, and quenching the fibres immediately thereafter in a coolingbath at a temperature not greater than 30 C.

In the process of the invention, the fibres may be stretched in steam byconventional methods, for example in tubes fed with direct steam betweenrollers rotating at different speeds, and are preferably stretched tonot less than five times their original length. After leaving thestretching tubes they are quenched immediately, i.e., with the minimumpracticable delay, in a cooling bath at less than 30 C. The cooling bathpreferably contains water, which may without disadvantage contain somedissolved alkali metal thiocyanate, through which the fibres areconducted, but it is also possible to quench the fibres by sprayingwater or other coolant on to them. Quenching may with advantage takeplace at lower temperatures than 30 C., and it may be found that thebest results are United States Patent 0 obtained below 10 C., althoughit is not normally necessary to employ temperatures lower than 0 C.

It may be desired to wash the fibres after quenching, for example at 40to 50 C. in water, whereafter they may be dried and subjected to furtherprocessing as desired.

The invention is illustrated by the following examples:

Example 1 An acrylonitrile copolymer containing 93 percent by weight ofacrylonitrile units in solution in aqueous sodium thiocyanate was spuninto fibres by coagulation with dilute aqueous sodium thiocyanate. Theresulting fibres were stretched to eight times their initial length insteam between rollers, and were passed into a bath containing distilledwater at 8 C., immediately upon leaving the last roller. They were thenwashed until they were substantially free from thiocyanate and dried.The fibres had a substantially uniform shrinkage of approximately 10percent and showed no observable fibrillation either initially or onsubsequent processing.

Example 2 A similar copolymer was spun and coagulated as in Example 1,and the fibres produced were stretched in steam to eight times theirinitial length, whereupon they were passed through a quenching spray ofdilute sodium thiocyanate at 10 C., so that the temperature of thefibres was reduced to below 30 C. The resulting fibres, after drying,had similar properties to those produced by the process of Example 1.

We claim:

1. In a process for the production of fibers from acrylonitrile polymersin which a polymer containing from to 97 percent by weight ofacrylonitrile units is spun into an aqueous coagulating bath to formfilaments, the improvement which consists essentially in removing saidfilaments from the bath, stretching said filaments in steam by at least5 times their original length and immediately thereafter quenching thefilaments by contact with a liquid bath consisting essentially of water,said liquid bath having a temperature between about 0 and 10 C., therebyto suppress the tendency of said filaments to fibrillate.

References Cited UNITED STATES PATENTS 2,558,731 7/1951 Cresswell264-182 3,097,054 7/ 1963 Routson et a1. 264-182 FOREIGN PATENTS 887,008l/1962 Great Britain.

JULIUS FROME, Primary Examiner. HERBERT M'INTZ, Assistant Examiner.

US. Cl. X.R.

